Power Recovery System Using A Rankine Power Cycle Incorporating A Two-Phase Liquid-Vapor Expander With Electric Generator

ABSTRACT

A power recovery system using the Rankine power cycle incorporating a two-phase liquid-vapor expander with an electric generator which further consists of a heat sink, a heat source, a working fluid to transport heat and pressure energy, a feed pump and a two-phase liquid-vapor expander for the working fluid mounted together with an electric generator on one rotating shaft, a first heat exchanger to transport heat from the working fluid to the heat sink, a second heat exchanger to transport heat from the heat source to the working fluid.

RELATED APPLICATIONS

This application is a divisional application of pending U.S. patentapplication Ser. No. 13/199,943, filed Sep. 13, 2011 entitled “POWERRECOVERY SYSTEM USING A RANKINE POWER CYCLE INCORPORATING A TWO-PHASELIQUID-VAPOR EXPANDER WITH ELECTRIC GENERATOR”, Attorney Docket No.EIC-901, which is a non-provisional application of and related to U.S.Provisional Patent Application Ser. No. 61/403,348 filed Sep. 13, 2010entitled POWER RECOVERY SYSTEM USING A RANKINE POWER CYCLE INCORPORATINGA TWO-PHASE LIQUID-VAPOR EXPANDER WITH ELECTRIC GENERATOR, AttorneyDocket No. EIC-901-P, which are both incorporated herein by reference intheir entirety, and claim any and all benefits to which they areentitled therefrom.

FIELD OF THE INVENTION

The present invention pertains to an LNG regasification system thatutilizes power recovery, and more specifically, to such systemincorporating a two-phase expander generator that generates electricalenergy during regasification.

BACKGROUND OF THE INVENTION

Liquefied natural gas, hereafter “LNG”, is natural gas that has beenconverted at least temporarily to liquid phase for ease of storage ortransport. LNG takes up about 1/600th the volume of natural gas in thevapor or gaseous phase. The reduction in volume makes it much more costefficient to transport over long distances where pipelines may or maynot exist. In certain cases where moving natural gas by pipeline is notpossible or economical, LNG can be transported by specially designedcryogenic sea vessels known as “LNG carriers” or “cryogenic roadtankers”.

The conventional regasification process for onshore and offshore plantsincorporates two major elements:

-   1. High-pressure send-out pumps to bring the pressure of the LNG up    from relatively low storage pressure through the vaporizer to    relatively high pipe line pressure; and-   2. The vaporizer/expander to transform the LNG into gaseous natural    gas.

The LNG regasification process consists of the steps of unloading LNGvessels at the receiving terminal and storing LNG in insulated tanks atatmospheric pressure at a temperature in the range of 111 Kelvin [K],which is around minus 170 Celsius [C]. During the regasificationprocess, LNG is pumped to a high pressure by a cryogenic, high-pressureLNG pump or similar equipment while it is still in the liquid state. TheLNG is then heated until it vaporizes into its gaseous state. In commoncommercial practice, the heat source used in regasification of LNG isprovided by local sea water. The naturally stored “heat” in sea water isa heat source for heating and vaporizing LNG.

Cryogenic high-pressure LNG pumps are used for pressurizing the fluid upto the high pipe line pressure while it is still in the liquid state.Typical dimensions for these types of pumps are 4 meters in height and 1meter in diameter, with as many as 12 or more centrifugal pump impellerstages, each of up to 300 mm or more diameter.

FIG. 1 (prior art) shows a particular design of an existinghigh-pressure, centrifugal LNG pump. Its design features the singlepiece, rotating axial shaft with integrally mounted multi-stage pumphydraulics and electrical induction motor. The thrust balancingmechanism is incorporated into the pump to eliminate high axial thrustforces on the bearings. The electrical induction motor is submerged inand cooled by LNG, and the ball bearings are lubricated and cooled byLNG.

General, high-pressure pump design criteria is summarized as follows:

Pump General Design Criteria Liquid LNG Model 6ECC-1212 Pump DesignPressure [bara] 133.4 Lowest Design Temperature [° C.] −168 OperatingTemperature [° C.] −147 Rated Flow [m³/hr] 287 Rated Differential Head[m] 2396 Rated Density [kg/m³] 417.417 Maximum Design Density [kg/m³]451.00

Typical LNG regasification plants require large heat sinks thatnecessitate large heat sources. Temperature differentials between heatsources, e.g., seawater, and heat sinks, e.g., LNG, are in the range of170° Celsius, thus providing feasible preconditions for an efficientrecovery of power. There have been past attempts to recover some of theinput energy used during the LNG regasification process. One commonlimitation is that the energy recovered using a common one-phase[liquid] turbine and generator combination, from just the vapor orgaseous state of LNG, is very ineffective. However, in a two-phase[liquid, gas] process, the combination of high pressure and mechanicalturbulence created and the presence of liquid droplets of LNG is highlycorrosive or abrasive, and will damage the equipment used in mostcurrent regasification plants.

The Rankine power cycle is a cycle that converts heat into work. Heat issupplied externally to a closed loop of working fluid, such as water.The working fluid is heated, vaporized, used to drive a steam turbine togenerate electrical power, re-condensed to liquid by cooling, and thecycle is repeated. This cycle generates about 80% of all electric powerused throughout the world, including virtually all solar thermal,biomass, coal and nuclear power plants.

The Rankine power cycle describes a model of steam operated heat enginemost commonly found in power generation plants. Common heat sources forpower plants using the Rankine power cycle are the combustion of coal,natural gas and oil, and nuclear fission.

There is nothing in the prior art that teaches a system which convertsheat from a heat source to work incorporated into an LNG regasificationprocess. The need exists to incorporate a reduction generator, where thework is further converted into electrical energy, to recovers some ofthe energy input to the LNG during the regasification process. There arecurrently no power plants in operation in which the working fluid is LNGand the heat source is mainly sea water, wherein the entire processoperates at a much lower temperature than that utilized in conventionalpower generation plants.

SUMMARY OF INVENTION AND ADVANTAGES

The present invention is a power recovery system using a Rankine powercycle, incorporating a compact design which consists of a pump, atwo-phase LNG expander and an induction generator, integrally mounted onone single rotating shaft. The present invention incorporates a powerrecovery system to partially regain the input energy used in the overallregasification process.

One object of the present invention is to provide an efficient andeconomical power recovery for LNG regasification plants.

An object and advantage of the present invention is that the expanderwork output is larger than the pump work input and the difference inwork is converted by the generator into electrical energy as powerrecovery.

Yet another object and advantage of the present invention is that thelosses of a separate pump motor are eliminated.

Yet a another object and advantage of the present invention is torecover and use the losses of the induction generator as a heat sourceto heat the working fluid, such as LNG or LPG, in addition to the heatfrom sea water and other heat sources.

Yet another object and advantage of the present invention is that anyleakages of the working fluid is within a closed loop and occurs onlybetween pump and expander.

Yet another object and advantage of the present invention is that anyleakages of the working fluid is minimized due to equal pressure on bothsides of the seal, and small leakages are within a closed loop and occuronly between pump, expander and generator.

Yet another object and advantage of the present invention is that theaxial thrust is minimized due to opposing directions of the thrustforces decreasing the bearing friction and increasing the bearing life.

Benefits and features of the invention are made more apparent with thefollowing detailed description of a presently preferred embodimentthereof in connection with the accompanying drawings, wherein likereference numerals are applied to like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (prior art) shows a particular design of an existinghigh-pressure, centrifugal LNG pump.

FIG. 2A (prior art) is a representative pressure-enthalpy diagram,hereafter “P-h diagram”, showing an Rankine power cycle with singlephase vapor expansion.

FIG. 2B is a representative P-h diagram showing the Rankine power cycleof an embodiment of the present invention with high vapor contenttwo-phase expansion.

FIG. 2C is a representative P-h diagram showing the Rankine power cycleof an embodiment of the present invention with low vapor contenttwo-phase expansion.

FIG. 3A is a representative exposed isometric view of a two-phaseexpander generator 300 of the present invention 100.

FIG. 3B is a representative partial isometric view of the two-phasehydraulic assembly 400 shown in FIG. 3A.

FIG. 3C is a representative enlarged isometric view of nozzle ring 402of the two phase hydraulic assembly 400 shown in FIG. 3A.

FIG. 3D is a representative enlarged isometric view of jet exducer 404of the two phase hydraulic assembly 400 shown in FIG. 3A.

FIG. 3E is a representative enlarged isometric view of reaction turbinerunner 406 of the two-phase hydraulic assembly 400 shown in FIG. 3A.

FIG. 3F is a representative enlarged isometric view of two-phaseexpander draft tube 408 of the two-phase hydraulic assembly 400 shown inFIG. 3A.

FIG. 4 is a representative schematic diagram showing the Rankine powercycle power recovery system of the present invention 200 using two-phaseexpansion.

FIG. 5A is a representative cross sectional view of an embodiment of apump two-phase expander generator of the present invention 100.

FIG. 5B is a representative cross sectional view of an alternativeembodiment of a pump two-phase expander generator of the presentinvention 100′.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The description that follows is presented to enable one skilled in theart to make and use the present invention, and is provided in thecontext of a particular application and its requirements. Variousmodifications to the disclosed embodiments will be apparent to thoseskilled in the art, and the general principals discussed below may beapplied to other embodiments and applications without departing from thescope and spirit of the invention. Therefore, the invention is notintended to be limited to the embodiments disclosed, but the inventionis to be given the largest possible scope which is consistent with theprincipals and features described herein.

Power Recovery:

LNG regasification plants require large heat sinks that necessitatelarge heat sources. The differences in temperature between the heatsources and the heat sinks are in the range of 170° Celsius providingthe preconditions for an efficient recovery of power. The Rankine powercycle is a thermodynamic cycle which converts heat into work. The heatis supplied externally to a closed loop with a particular working fluid,and also requires a heat sink. This cycle generates about 80% of allglobal electric power.

FIG. 2A (prior art) is a representative pressure-enthalpy diagram,hereafter “P-h diagram”, showing an Rankine power cycle with singlephase vapor expansion. The Rankine power cycle is shown using a typicalMollier diagram with the pressure p over the enthalpy h.

As shown in FIG. 2A, the ideal Rankine power cycle with single phasevapor expansion consists of the following four process steps:

-   -   1->2 Isentropic compression of the liquid fluid to a high        pressure in a pump. The working fluid is pumped from low to high        pressure, as the fluid is a liquid at this stage the pump        requires little input energy.    -   2->3 Constant high pressure heat addition in a boiler to        completely vaporize the fluid. The high pressure liquid enters a        boiler where it is heated at constant pressure by an external        heat source to become a dry saturated vapor, thus one-phase. The        input energy required can be easily calculated using Mollier        diagram or h-s chart or enthalpy-entropy chart also known as        steam tables.    -   3->4 Isentropic expansion in a turbine gas expander to low        pressure. The dry saturated vapor expands through a turbine,        generating [recovering] power. This decreases the temperature        and pressure of the vapor, and some condensation may occur. The        output in this process can be easily calculated using the        enthalpy-entropy chart or the steam tables.    -   4->1 Constant low pressure heat rejection in a condenser to        re-liquefy the fluid. The wet vapor then enters a condenser        where it is condensed at a constant temperature to become a        saturated liquid.

The Rankine power cycle illustrated in FIG. 2A represents a one-phaseexpansion which happens in most power plants as current turbines andexpanders do not tolerate highly pressurized working liquid dropletsduring step 3 to 4.

The symbols h₁, h2, h3 and h4 in FIGS. 2A, 2B and 2C represent theenthalpy of steps 1, 2, 3 and 4, respectively. The thermodynamicefficiency η_(therm) of any Rankine power cycle is the ratio of the netpower output Wnet to the heat input qin. The net power output w_(out)from the expander and the work input w_(in) to the pump. η_(therm) iscalculated as follows:

Specific work input to pump: w_(in) = h2 − h1 Specific work output fromexpander: w_(out) = h3 − h4 Specific heat input from step 2 to step 3:q_(in) = h3 − h2 Net power output: w_(net) = w_(out) − w_(in)The thermodynamic efficiency of the ideal cycle is the ratio of netpower output to heat input:

η_(therm) =w _(net) /q _(in)

η_(therm)=1−(h4−h1)/(h3−h2)

In one embodiment, the higher the thermodynamic efficiency of theRankine power cycle, the more power is recovered.

In an ideal Rankine power cycle, the pump and turbine would beisentropic, i.e., the pump and turbine would generate no entropy andhence maximize the net work output. Processes 1-2 and 3-4 would berepresented by vertical lines on the T-S diagram and more closelyresemble that of the Carnot cycle.

FIG. 2B is a representative P-h diagram showing the Rankine power cycleof an embodiment of the present invention with high vapor contenttwo-phase expansion. The two-phase fluid ideal Rankine power cycle withliquid-vapor two-phase expansion consists basically of the same foursteps 1 to 4, with the difference that the pressurized liquid is onlypartially vaporized thus remaining within the saturation dome. Thus, instep 3 the isentropic expansion of the liquid-vapor mixture is achievedin a two-phase fluid expander. Since both (h4−h1) and (h3−h2) decrease,the thermodynamic efficiency η_(therm) increases for the Rankine powercycle.

FIG. 2C is a representative P-h diagram showing the Rankine power cycleof an embodiment of the present invention with low vapor contenttwo-phase expansion. As h3 and h4 continue to shift towards the pressureaxis, the pressurized working fluid in step 3 is heated to a lowertemperature. Thus, lower heat input (h3−h2) is required and the vaporcontent of the working fluid during step 3 is higher compared to thatshown in the Rankine power cycle of FIG. 2B. In turn, the heat output(h4−h1) during step 4 and 1 also decreases. The work output (h3−h4)remains in a relatively consistent range, hence the overallthermodynamic efficiency increases. Theoretically, the further step 3and step 4 are shifted towards the pressure axis, the more efficient theRankine power cycle will be. In reality, the higher the vapor content ofthe working fluid in step 3, the more damage likely to be caused to theturbines and expanders by the liquid present in the working fluid.

Two-Phase Expander Generator:

FIG. 3A is a representative exposed isometric view of a two-phaseexpander generator 300 of the present invention 100. FIG. 3B is arepresentative partial isometric view of the two-phase hydraulicassembly 400 shown in FIG. 3A. In one embodiment, the two-phase expandergenerator 300 is used to perform step 3 to step 4 of the two-phaseRankine power cycle in FIGS. 2B and 2C. The main reason that thetwo-phase expander generator 300 can tolerate a working fluid havinghigh vapor content is that its design enables the kinetic energy of thehigh pressure two-phase working fluid to dissipate at the very end andtop portion in the two-phase hydraulic assembly 400, hence minimizingphysical harm and corrosion to the equipment.

In one embodiment, the two-phase expander generator 300 of the presentinvention consists of a two-phase hydraulic assembly 400 mounted on arotating, axial shaft 310. As shown in FIG. 3B, two-phase hydraulicassembly 400 further consists of non-rotating nozzle ring 402 on thebottom, followed by the rotating reaction turbine runner 406 with jetexducer 404 mounted on top. On top of jet exducer 404, the non-rotatingtwo-phase draft tube 408 is mounted. In one embodiment, reductiongenerator 306 is also mounted on rotating axial shaft 310 underneath thetwo-phase hydraulic assembly 400. The entire embodiment is completelyencased inside pressurized containment vessel 304. As best shown in FIG.3A, high pressure working fluid is pumped into two-phase expandergenerator 300 at lower inlet 302. The working fluid travels upwardpassing induction generator 306, losing pressure along the way. It thenenters two-phase hydraulic assembly 400 at nozzle ring 402, dissipatingits internal and kinetic energy along the way to drive rotating axialshaft 310 and exits at upper outlet nozzle 308 with less pressure andlower enthalpy. The rotation of rotating axial shaft 310 drivesinduction generator 306, generating electrical energy, i.e., powerrecovery.

FIG. 3C is a representative enlarged isometric view of the nozzle ring402 of the two phase hydraulic assembly 400 shown in FIG. 3A. In oneembodiment, the stationery or non-rotating nozzle ring 402 has upperplate 422 enclosing converging nozzles 420 to generate a high velocityvortex flow of the incoming working fluid.

FIG. 3D is a representative enlarged isometric view of the reactionturbine runner 406 of the two-phase hydraulic assembly 400 shown in FIG.3A. In one embodiment, the rotating reaction turbine runner 406 andstationary housing portion 430 converts the angular fluid momentum ofthe vortex flow coming out of nozzle ring 402 into shaft torque ofrotating axial shaft 310.

FIG. 3E is a representative enlarged isometric view of the jet exducer404 of the two phase hydraulic assembly 400 shown in FIG. 3A. As shownin FIG. 3E, the rotating jet exducer 404 is a radial outflow turbinemounted on top of reaction runner 406 for generating additional rotatingaxial shaft 310 torque by an angular fluid momentum in a directionopposite to that of the nozzle ring 402 with a near isentropic,two-phase expansion to the lower pressure of exiting working fluid.

FIG. 3F is a representative enlarged isometric view of a two-phaseexpander draft tube 408 of the two-phase hydraulic assembly 400 shown inFIG. 3A. As shown in FIG. 3F, the non-rotating two-phase draft tube 408recovers energy by converting the remaining rotational kinetic energy ofthe working fluid into static pressure energy, or “thrust”.

Power Generation/Recovery:

The generated theoretical maximum mechanical specific power per massP_(max) of two-phase expander generator 300 driven by ideal workingfluids is equal to the product of specific volumetric flow per secondv_(s) and the pressure difference Δp [P_(high)−P_(low)] between inlet302 and outlet 308 as follows:

P _(max) [J/(kgs]=v_(s)[m³/(kgs)]Δp[Pa]

However, for expander generator 300 driven by real fluids, likecompressible liquids, gases, and liquid-vapor mixtures, the specificvolume v in m³/kg is not constant and changes with the momentarypressure p and the enthalpy h as follows:

v=v[h,p]

The theoretical maximum differential enthalpy Δh for a smalldifferential expansion pressure dp is described by the followingdifferential equation:

Δh=v[h,p]Δp

The generated theoretical maximum specific power is then calculated byintegrating this differential equation Δh=h[p]. The corresponding poweroutput in kJ/s is Δh in kJ/kg multiplied by the mass flow in kg/s.

Two-Phase Rankine Power Cycle:

For power recovery using a two-phase fluid Rankine power cycle, as bestshown in FIGS. 2B and 2C, in LNG regasification plants, several fieldproven working fluids are available and used in similar applications. Asbest shown in FIG. 4, to achieve a higher thermodynamic efficiencyη_(therm), the two-phase working fluid passes through two heatexchangers 202 and 204, and one pump two-phase expander generator 100.

In one embodiment, pump two-phase expander generator 100 of the presentinvention resembles two-phase expander generator 300 as best shown inFIGS. 3A to 3F. The one added embodiment is a pump 502. The compactassembly comprises a pump 502, a two-phase expander 506 and an inductiongenerator 504 integrally mounted on one rotating shaft 508.

FIG. 4 is a representative schematic diagram showing the Rankine powercycle power recovery system of the present invention 200 using two-phaseexpansion. Process steps shown in FIG. 4 correspond to the fourdescribed process steps of the two-phase Rankine power cycle shown inFIGS. 2B and 2C. The system of the present invention 200 consists ofheat sink 202, heat source 204 and pump two-phase expander generator 100that further consists of pump 502, induction generator 504 and two-phaseexpander 506.

Step 1 to 2:

Working fluid in liquid phase enters pump 502 and by receiving workinput, pump 502 pressurizes the liquid single phase working fluid fromlow pressure P_(LOW) to high pressure P_(HIGH).

Step 2 to 3:

The pressurized single phase working fluid passes through generator 504internally and working fluid is heated and partially vaporized bypassing through induction generator 504, as represented by point A inFIG. 2C. It subsequently flows out of pump two-phase expander generator100 to an outside heat source 204. In one embodiment, heat source is seawater which has a much higher temperature than the working fluid, LNG orliquid propane gas, LPG. In other embodiments, the heat provided at theheat source 204 can be from other sources depending on theregasification plant.

Step 3 to 4:

The pressurized and heated two-phase saturated working fluid in step 3flows back to the pump two-phase expander generator 100 at two-phaseexpander 506 where it expands and drops in pressure from high pressureP_(high) to low pressure P_(low), generating a work output. Part of thekinetic energy and internal energy of the heated two-phase saturatedfluid is converted to electrical energy when working fluid fromtwo-phase expander 506 drives induction generator 504.

Step 4 to 1:

The low pressure two-phase saturated working fluid flows out of pumptwo-phase expander generator 100 at two-phase expander 506 and passesthrough an external heat sink 202. The process of regasification of LNGoccurs at heat sink 202. The low pressure two-phase saturated workingfluid takes heat from the colder LNG at the heat sink 202. While theworking fluid condenses from saturated liquid-vapor two-phase tonon-saturated liquid single phase, it serves as the heat source for theLNG regasification process and the LNG at the heat sink 202 is heatedand partly or completely vaporized.

FIG. 5A is a representative cross sectional view of an embodiment of apump two-phase expander generator of the present invention 100. As bestshown in FIG. 5A, pump two-phase expander generator 100 is a compactassembly consisting of feed pump 502 at the bottom of the stack,induction generator 504 in the middle, and two-phase expander 506 at thetop, all integrally mounted on one rotating axial shaft 508. The lowerpart of the system 100 is completely encased in a pressurizedcontainment vessel 530. Pump two-phase expander generator 100 canperform Step 1 to 2 and Step 3 to 4 of the two-phase Rankine power cyclebest described in FIGS. 2B and 2C. As best shown in FIG. 5A, lowpressure working fluid in liquid state enters the pump 502 at the lowerinlet nozzle 520, exits the pump at side outlet 522 to heat source 204and passes internally through induction generator 504 housing, coolinginduction generator 504, thus recovering the heat losses of generator504. The working fluid exits through side outlet 526 to heat source 204.After passing through external heat source 204, the saturated two-phaseworking fluid reenters pump two-phase expander generator 100 at sideinlet 524 and the high pressure saturated two-phase working fluidexpands across two-phase expander 506, generating work and drivingrotating shaft 508 and subsequently pump 502 and induction generator504. The low pressure saturated working fluid then flows out of pumptwo-phase expander generator 100 through side outlet 528 to heat sink202 where its internal energy is dissipated by passing across colder LNGat heat sink 202. The working fluid is thus converted back to lowpressure liquid state. The cycle begins again as low pressure liquidphase working fluid reenters pump two-phase expander generator 100 atinlet 520.

In one embodiment, during start-up of pump two-phase expander generator100 of the present invention, the induction generator 504 operates as aninduction motor below the synchronous speed to provide power for feedpump. When the shaft power of the two-phase expander 506 is greater thanthe shaft power of the feed pump 502, the induction motor operates inthe generator mode above the synchronous speed.

FIG. 5B is a representative cross sectional view of an alternativeembodiment of a pump two-phase expander generator of the presentinvention 100′. In one alternative embodiment, the pressurized singlephase working fluid passes directly from the pump 502′ through theinduction generator 504′ housing, thus cooling the induction generator504′, and then exits to the side to pass though the heat source 204. Inboth embodiments, the leakage flow through the seal and the axial thrustis minimized due to equal pressure on both sides of the seal andopposing directions of the axial thrust forces.

The following advantages of the pump two-phase expander generator 100 ofthe present invention can be realized:

-   1. The expander work output is larger than the pump work input and    the difference in work is converted by the generator into electrical    energy.-   2. The expander work output is larger than the pump work input and    the difference in work is converted into electrical energy by the    generator.-   3. The losses of a separate pump motor are eliminated.-   4. The losses of the induction generator are recovered and used, in    addition to the heat from sea water and other heat sources, to heat    the working fluid.-   5. Any leakage of the working fluid is within a closed loop and    occurs only between pump and expander.-   6. Any leakage of the working fluid is minimized due to equal    pressure on both sides of the seal, and small leakages are within a    closed loop and occur only between pump, expander and generator.-   7. The axial thrust is minimized due to opposing directions of the    thrust forces decreasing the bearing load and increasing the bearing    life.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the present invention belongs. Although any methods andmaterials similar or equivalent to those described can be used in thepractice or testing of the present invention, the preferred methods andmaterials are now described. All publications and patent documentsreferenced in the present invention are incorporated herein byreference.

While the principles of the invention have been made clear inillustrative embodiments, there will be immediately obvious to thoseskilled in the art many modifications of structure, arrangement,proportions, the elements, materials, and components used in thepractice of the invention, and otherwise, which are particularly adaptedto specific environments and operative requirements without departingfrom those principles. The appended claims are intended to cover andembrace any and all such modifications, with the limits only of the truepurview, spirit and scope of the invention.

1. A power recovery system for recovery of part of the required energyinput during regasification of LNG using a Rankine power cycle, thepower recovery system comprising: a working fluid; a system containingthe working fluid in a closed loop; a pump two-phase liquid-vaporexpander generator comprising: a stationary outer housing portion havingone lower inlet, one side inlet, a plurality of side outlets, the lowerinlet letting in the liquid-phase working fluid, and the side outletlocated at an upper end of the outer housing, letting out expandedtwo-phase working fluid; an inner feed pump on top of the lower inlet,mounted on a rotating center shaft extending most of the length of thepump two-phase liquid-vapor expander generator, the pump pressurizingthe liquid-phase working fluid entering from the lower inlet; an innerinduction generator further having a casing, mounted on said rotatingcenter shaft, on top of the pump, the induction generator driven by therotating center shaft, generating electricity as a result, thepressurized liquid-phase incoming working fluid passing through thecasing of the induction generator and flowing out through the sideoutlet for heating; an inner two-phase hydraulic assembly mounted onsaid rotating center shaft on top of the induction generator forexpanding the heated and pressurized two-phase incoming working fluidfrom the side inlet, converting angular momentum and internal energy ofthe heated and pressurized two-phase incoming working fluid into torque,driving the rotating center shaft; a casing containing the entiretwo-phase hydraulic assembly; a stationery flat circular nozzle ringportion at the bottom of the two-phase hydraulic assembly, the nozzlering portion further having a center aperture and a plurality ofconverging nozzles on its rim for generation of high velocity vortexflow of the pressurized and heated two-phase working fluid as it flowsthrough; and a rotating turbine runner portion sitting on top of theaperture of the nozzle ring portion and mounted on and driving therotating center shaft as the turbine runner portion converting angularmomentum of the high velocity vortex flow of the two-phase working fluidinto torque; a heat source connected to the pump two-phase liquid-vaporexpander generator via the pipe system, the heat source heating thepressurized working fluid into higher vapor content, the heated andpressurized two-phase working fluid then re-entering the pump two-phaseliquid-vapor expander generator at the two-phase liquid-vapor expanderwherein the heated and pressurized two-phase working fluid expands anddrives the rotating center shaft, and subsequently the inductiongenerator, the expanded two-phase working fluid flowing out of the pumptwo-phase liquid-vapor expander for cooling and condensation; and a heatsink connected to the pump two-phase liquid-vapor expander generator viathe pipe system, the heat sink cooling the expanded two-phase workingfluid such that the two-phase working fluid is condensed back to theliquid state, the liquid-phase working fluid then re-entering the pumptwo-phase liquid-vapor expander generator at the feed pump, andrepeating the cycle.
 2. The LNG regasification power recovery system ofclaim 1 in which the heat source is sea water.
 3. The LNG regasificationpower recovery system of claim 1 in which the heat source is steam. 4.The LNG regasification power recovery system of claim 1 in which theheat sink is pressurized liquefied natural gas.
 5. The LNGregasification power recovery system claim 1 in which the working fluidis liquefied natural gas.
 6. A two-phase liquid-vapor expander generatorfor expanding working fluid and generating electricity during LNGregasification processes, the two-phase liquid-vapor expander generatorcomprising: a stationary outer housing portion having an inlet and anoutlet, the inlet located at a lower end on one side of the outerhousing portion, letting in the heated and pressurized two-phase workingfluid, and the outlet located at an upper end, letting out the expandedtwo-phase working fluid; and an inner induction generator mounted on arotating center shaft, the induction generator driven by the rotatingcenter shaft, generating electricity as a result; and an inner two-phasehydraulic assembly mounted on said rotating center shaft on top of theinduction generator, the hydraulic assembly further comprising: a casingcontaining the entire hydraulic assembly; a stationery flat circularnozzle ring portion at the bottom of the hydraulic assembly, the nozzlering portion further having a center aperture and a plurality ofconverging nozzles on its rim for generation of high velocity vortexflow of the pressurized and heated two-phase working fluid as it flowsthrough; a rotating turbine runner portion sitting on top of theaperture of the nozzle ring portion, the hydraulic assembly forexpanding the pressurized incoming two-phase working fluid, convertingangular momentum and internal energy of the incoming two phase workingfluid into torque, driving the rotating center shaft.
 7. A method forpower recovery using a two-phase fluid Rankine power cycle in an LNGregasification plant, the method comprising: passing the working fluidthrough 2 heat exchangers and a pump two-phase expander generator, thepump two-phase expander generator comprising: a stationary outer housingportion having one lower inlet, one side inlet, a plurality of sideoutlets, the lower inlet letting in the liquid-phase working fluid, andthe side outlet located at an upper end of the outer housing, lettingout expanded two-phase working fluid; an inner feed pump on top of thelower inlet, mounted on a rotating center shaft extending most of thelength of the pump two-phase liquid-vapor expander generator, the pumppressurizing the liquid-phase working fluid entering from the lowerinlet; an inner induction generator further having a casing, mounted onsaid rotating center shaft, on top of the pump, the induction generatordriven by the rotating center shaft, generating electricity as a result,the pressurized liquid-phase incoming working fluid passing through thecasing of the induction generator and flowing out through the sideoutlet for heating; an inner two-phase hydraulic assembly mounted onsaid rotating center shaft on top of the induction generator forexpanding the heated and pressurized two-phase incoming working fluidfrom the side inlet, converting angular momentum and internal energy ofthe heated and pressurized two-phase incoming working fluid into torque,driving the rotating center shaft; a casing containing the entiretwo-phase hydraulic assembly; a stationery flat circular nozzle ringportion at the bottom of the two-phase hydraulic assembly, the nozzlering portion further having a center aperture and a plurality ofconverging nozzles on its rim for generation of high velocity vortexflow of the pressurized and heated two-phase working fluid as it flowsthrough; and a rotating turbine runner portion sitting on top of theaperture of the nozzle ring portion and mounted on and driving therotating center shaft as the turbine runner portion converting angularmomentum of the high velocity vortex flow of the two-phase working fluidinto torque; such that the following steps are performed in thefollowing sequence; in a first step, with work input, the pump, P,pressurizes the liquid single phase working fluid from low pressure tohigh pressure; in a second step, the pressurized single phase workingfluid is heated and partially vaporized by passing through thegenerator, G, and the heat exchanger with the heat provided by sea wateror other heat sources; in a third step, the pressurized and heatedtwo-phase saturated working fluid expands from high-pressure tolow-pressure across the two-phase expander, T, generating a work output; and in a fourth step, the low pressure two-phase saturated workingfluid passes through a heat exchanger with the heat sink, the LNG forregasification, such that the working fluid condenses from saturatedliquid-vapor two-phase to non-saturated, liquid single phase.
 8. Themethod of claim 7 in which the heat source is steam and/or sea water. 9.The method of claim 7 in which the heat sink is pressurized liquefiednatural gas.
 10. The method of claim 7 in which the working fluid isliquefied natural gas.
 11. A power recovery system for recovery of partof the required energy input during regasification of LNG using aRankine power cycle, the power recovery system comprising: a workingfluid; a system containing the working fluid in a closed loop; a pumptwo-phase liquid-vapor expander generator further comprising a feedpump, an induction generator and a two-phase liquid-vapor expander, allmounted on a common, rotating axial shaft, the expander generatorfurther comprising: a casing containing the entire expander generatorassembly; a stationery flat circular nozzle ring portion at the bottomof the expander generator assembly, the nozzle ring portion furtherhaving a center aperture and a plurality of converging nozzles on itsrim for generation of high velocity vortex flow of the pressurized andheated two-phase working fluid as it flows through; a rotating turbinerunner portion sitting on top of the aperture of the nozzle ringportion, the feed pump pumping the incoming liquid-phase working fluidto a high pressure, the pressurized liquid-phase working fluid thenpassing through the induction generator, partly heated and vaporizedtherein and then flowing out the pump two-phase liquid-vapor expandergenerator for further heating; a heat source connected to the pumptwo-phase liquid-vapor expander generator via the pipe system, the heatsource heating the pressurized working fluid into higher vapor content,the heated and pressurized two-phase working fluid then re-entering thepump two-phase liquid-vapor expander generator at the two-phaseliquid-vapor expander wherein the heated and pressurized two-phaseworking fluid expanded and driving the rotating center shaft, andsubsequently the induction generator, the expanded two-phase workingfluid flowing out of the pump two-phase liquid-vapor expander forcooling and condensation; and a heat sink connected to the pumptwo-phase liquid-vapor expander generator via the pipe system, the heatsink cooling the expanded two-phase working fluid, the two-phase workingfluid condensed back to the liquid state, the liquid-phase working fluidthen re-entering the pump two-phase liquid-vapor expander generator atthe feed pump, and repeating the cycle.
 12. The LNG regasification powerrecovery system of claim 11 in which the heat source is sea water. 13.The LNG regasification power recovery system of claim 11 in which theheat source is steam.
 14. The LNG regasification power recovery systemof claim 11 in which the heat sink is pressurized liquefied natural gas.15. The LNG regasification power recovery system claim 11 in which theworking fluid is liquefied natural gas.
 16. A method for power recoveryusing a two-phase fluid Rankine power cycle in an LNG regasificationplant, the method comprising the following steps: passing the workingfluid through 2 heat exchangers and a pump two-phase expander generator,the pump two-phase expander generator consisting of a compact assemblyof a pump, a two-phase expander and an induction generator integrallymounted on one rotating, axial shaft, the expander generator furthercomprising: a casing containing the entire expander generator; astationery flat circular nozzle ring portion at the bottom of theexpander generator, the nozzle ring portion further having a centeraperture and a plurality of converging nozzles on its rim for generationof high velocity vortex flow of the pressurized and heated two-phaseworking fluid as it flows through; a rotating turbine runner portionsitting on top of the aperture of the nozzle ring portion, such that thefollowing steps are performed in the following sequence: in a firststep, with work input, the pump, P, pressurizes the liquid single phaseworking fluid from low pressure to high pressure; in a second step, thepressurized single phase working fluid is heated and partially vaporizedby passing through the generator, G, and the heat exchanger with theheat provided by sea water or other heat sources; in a third step, thepressurized and heated two-phase saturated working fluid expands fromhigh-pressure to low-pressure across the two-phase expander, T,generating a work out put; and in a fourth step, the low pressuretwo-phase saturated working fluid passes through a heat exchanger withthe heat sink, the LNG for regasification, such that the working fluidcondenses from saturated liquid-vapor two-phase to non-saturated, liquidsingle phase.
 17. The LNG regasification power recovery system of claim16 in which the heat source is sea water.
 18. The LNG regasificationpower recovery system of claim 16 in which the heat source is steam. 19.The LNG regasification power recovery system of claim 16 in which theheat sink is pressurized liquefied natural gas.
 20. The LNGregasification power recovery system claim 16 in which the working fluidis liquefied natural gas.